This invention relates to valves, and more particularly, to valves having adjustable valve seats. Relevant prior art includes the following U.S. Pat. Nos: White 3,144,040; Killian 3,197,174; Fawkes 3,393,697; and Kurkjian 3,412,975.
In large valves, such as butterfly valves which frequently have fluid flow passages of diameters of two feet and greater, considerable difficulty has been encountered in obtaining uniform sealing contact between a valve member and a valve seat when the former is in a closed position. The valve seats typically employed are of resilient, flexible material that is much softer than the material of which the valve member is formed, and are designed to deform slightly when the valve member is moved to a closed position to provide the requisite sealing contact. If the sealing surface of the valve seat is not properly located with respect to the valve, the valve will either leak or accelerated wear of the valve seat will occur. For example, when the valve seat is improperly located so that something less than the desired deformation occurs when the valve member is moved to the closed position, the possibility of leakage exists. On the other hand, when the valve seat is too close to the valve member and must be deformed more than the optimal amount, the difference in material hardness can cause the accelerated wear of the valve seat with the result that valve failure is more prone to occur.
There have been a variety of proposals over the years for adjustable valve seats, and the four above-identified United States patents indicate various ones of such proposals. Such structures have proved to be quite successful in accomplishing their intended purpose. However, the same generally require some means of attachment to a valve body requiring machining operations for receipt of threaded fasteners or the like. Thus, the valves made according to such patents tend to be somewhat more expensive than would be desirable due to the need for such machining operations.